Driving a MEMS oscillator through a secondary set of support arms

ABSTRACT

A MEMS oscillator, such as a MEMS scanner, has an improved and simplified drive scheme and structure. Drive impulses may be transmitted to an oscillating mass via torque through the support arms. For multi-axis oscillators drive signals for two or more axes may be superimposed by a driver circuit and transmitted to the MEMS oscillator. The oscillator responds in each axis according to its resonance frequency in that axis. The oscillator may be driven resonantly in some or all axes. Improved load distribution results in reduced deformation. A simplified structure offers multi-axis oscillation using a single moving body. Another structure directly drives a plurality of moving bodies. Another structure eliminates actuators from one or more moving bodies, those bodies being driven by their support arms.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/984,327 filed Nov. 9, 2004, which claims priority under 35 U.S.C.119(e) to U.S. Provisional Application Ser. No. 60/571,133, filed on May14, 2004.

FIELD OF THE INVENTION

The present invention relates to MEMS devices and scanners and scannedbeam systems that use MEMS scanners, and more particularly to MEMSoscillators having actuators with multiplexed drive signals.

BACKGROUND OF THE INVENTION

MEMS (Micro electro mechanical system) devices may be used in manyapplications including rear and front projection scanned beam displays,scanned beam image capture devices, optical gyroscopes, accelerometers,and other applications. In addition to displays that project an imageonto a conventional opaque or translucent viewing screen, scanned beamdisplays can include retinal scanning displays (RSDs) and heads-updisplays (HUDs). Scanned beam image capture applications includeone-dimensional (1D) or linear scanning devices such as linear bar codescanners and two-dimensional (2D) image capture devices such as 2D barcode or omnidirectional linear bar code imagers, 2D bar code scanners,confocal microscopes, microprobes, medical imaging systems, and others.

For cases where the MEMS device is used to scan a beam of light, it isfrequently called a MEMS scanner or beam deflector. MEMS scanners mayoperate resonantly or non-resonantly, and may scan in one or a pluralityof axes.

MEMS devices may carry light emitters directly or alternatively maydeflect a beam through a scan angle. In beam deflection applications,one or more scan plates have a reflective surface that is used to scanan impinging beam over a field of view. The reflective surface mayinclude a plated reflective metal such as gold or aluminum, a dielectricstack, bare silicon, or other materials depending upon wavelength andother application issues.

2D scanning may be achieved by arranging a pair of 1D scanners withtheir axes of rotation at substantially right angles to one another.Alternatively, 2D scanners may use a single mirror that is driven torotate around both scanning axes. When a single mirror is used to scanin two axes, a gimbal ring may be used to allow appropriate rotation.Frequently, 2D scanners include an inner scan plate carrying a mirrorthat performs a fast scan with an outer gimbal ring performing a slowscan. Conventionally, the fast scan sweeps back and forth horizontallyacross the field of view (FOV) while the slow scan indexes down the FOVby one or two lines. Such systems may be termed progressive scansystems. In such systems the fast scan operates at a relatively highscan rate while the slow scan operates at a scan rate equal to the videoframe rate. In some applications, the fast scan operates resonantlywhile the slow scan provides a substantially sawtooth pattern, scanningprogressively down the frame for a (large) portion of the frame time andthen flying back to the top of the frame to start over. In otherapplications, interleaved sawtooth scanning, triangular wave scanning,sinusoidal scanning and other waveforms are used to drive one or bothaxes.

Although this document frequently refers to a fast scan direction ashorizontal (rotating about a vertical scan axis) and a slow scandirection as vertical (rotating about a horizontal scan axis), it mustbe realized that such a convention is not limiting. The teaching appliessimilarly to systems with fast and slow scans in the vertical andhorizontal directions, respectively, as well as other directions.

In progressive scan systems, the beam may be scanned unidirectionally orbidirectionally depending upon the desired resolution, frame rate, andscanner capabilities. Bi-directionally scanned systems may suffer fromraster pinch as described by Gerhard et al in U.S. Pat. No. 6,140,979entitled Scanned Display with Pinch, Timing, and Distortion Correction.One approach to compensating for raster pinch is to add a correctionmirror that corrects the beam path to more nearly approximate an idealraster pattern.

More recently, work by the applicant has focused on alternative scanpatterns that scan the beam in a Lissajous scan pattern over the FOV.Lissajous scan patterns have an advantage in being able to operate theMEMS scanner resonantly in both axes, thus reducing power consumption.Such systems may also have reduced torque requirements and may thus bemade smaller and have other advantages.

Various actuation technologies for MEMS scanners have been disclosed.Electrocapacitive drive scanners include both rear drive pad and combdrive architectures. Magnetic drive scanners include moving coil andmoving magnet types. Other technologies include thermal, piezoelectric,and impact motor drives. Rotation may be constrained by torsion arms,bending flexures and other arrangements. Electrocapacitive drive systemsare sometimes referred to as electrostatic in the literature. Bendingflexures are popularly referred to as cantilever arms.

Frequently, two or more drive schemes are combined to provideindependent drive in two or more axes. For example, the Gerhard et alpatent listed above shows a MEMS scanner with a fast scan axis that ispowered electrocapacitively and a slow scan axis that is poweredmagnetically. The need to provide independent drive actuators for eachaxis has heretofore limited size reductions as well as the number ofaxes.

Another aspect of MEMS oscillator requirements frequently includes theneed to monitor device motion or angle. Various schemas have beenproposed and used including piezo-resistive and optical feedback.

Overview

According to aspects of the present invention, a superior actuatordesign may be applied to MEMS devices. Additionally, according to otheraspects, structures, functionality, performance and cost may beimproved.

According to one embodiment, a plurality of actuator mechanisms may becoupled in series or in parallel. Each actuator mechanism may be pairedwith an oscillator component having a characteristic resonance frequencyand amplification factor. A single composite signal containing drivesignals for each of the actuator mechanisms may be used to actuate theactuators. The actuator responds to one or more specific drive signalcomponents based on the resonance frequency and amplification factorcharacteristics of its paired oscillator component.

According to some embodiments, the plurality of actuator mechanisms maybe electrically coupled through wires. In other embodiments, theplurality of actuator mechanisms may be coupled wirelessly through, forexample, an electromagnetic or acoustic interface. Electromagneticinterfaces may include RF, microwave, infrared light, visible light,ultraviolet light, or other forms of radiation.

According to other embodiments, various stationary magnet designs may beused to improve coupling of a moving coil scan plate to the magneticfield. The stationary magnets may be permanent magnets orelectromagnets.

According to another embodiment, a single axis magnetic field may beused to drive scanning in two or more non-parallel axes. The magneticfield may be oriented to be transverse to each of the axes. The angle ofthe magnetic field may be optimized according to the systemrequirements. Response variables include minimization of peak current,minimization of power consumption, maximization of torque in one or moreof the axes, minimization of size of one or more of the drive coils,minimization of response time to a signal input, matching of oscillationamplitudes, selection of phase relationships between frequencycomponents of the drive signal, and matching of resonant andnon-resonant drive schemas.

According to another embodiment, 2D scanning may be realized using astructure having one or more flexures that allow rotation in two or moreaxes to eliminate the gimbal ring.

According to another embodiment, a sensing coil may be used to determinecomponent position and movement. The sensing coil may be formed using noadditional mask layers by forming crossovers and crossunders in the coillayers. The sensing coil is made continuous by using a crossunder in theactuator coil conductor layer. The actuator coil is made continuous byusing a crossover in the sensing coil conductor layer. A dielectriclayer separates the conductor layers.

According to another embodiment, portions of the MEMS scanner aremechanically coupled to be driven in sympathetic resonance. In thisdocument, the term sympathetic resonance is to be understood to refer tothe phenomenon whereby slight movement by one element of a MEMS systemis mechanically communicated to a second element of the system, thesecond element being thus driven to relatively greater amplitudemovement by virtue of its resonant behavior. Such movement may be drivenon-resonance or off-resonance, as will be explained herein. Vibrationsin one portion of the scanner get transmitted and amplified by theresonance and amplification factor of a second portion of the scanner.The motion of first portion of the scanner receives negligible inputfrom the portion of the signal intended for the second portion of thescanner. The second portion of the scanner may be driven to substantialamplitude in sympathetic oscillation.

According to another embodiment, attaching the surface to flexuresthrough a suspension may minimize deformation of an active surface. Insome embodiments, MEMS scan plates or portions thereof are driven torotate through torsion arms. The torsion arms undergo significantstrain. Spreading the torsional load over a torque distribution membertermed a suspension reduces strain in the active surface. The activesurface may comprise a mirror, one or more emitters, or other featuresthat benefit from maintaining a predetermined shape.

According to another embodiment, a MEMS scanner may be driven entirelysympathetically with little motion of the actuator in the axis ofoscillation of the actuator. One or more actuators may be affixed tostationary surfaces. Periodic impulses of the actuator are mechanicallytransmitted across the MEMS structure. Portions of the MEMS device arethus driven to oscillate to a desired amplitude via mechanical couplingthrough the device.

The terms oscillator and scan plate are used herein somewhatinterchangeably. Either term generally refers to a structure of a MEMSdevice that may be driven through a periodic motion. A scan plate may bedriven with a sinusoidal periodicity that may be referred to asoscillation. In addition, structures such as gimbal rings that impartfreedom of motion in a plurality of axes, combined with the additionalstructures suspended therefrom, may be thought of as oscillatingassemblies. In other embodiments according to the invention, structuressuch as gimbal rings and scan plates may be driven in motions that arenot simply sinusoidal, but rather contain higher order sinusoidalcomponents that cooperate to confer motion approximating a sawtooth,square, triangular, or other waveform.

According to another embodiment, drive signals for various dimensions ofmovement by a MEMS device may be combined into a single composite drivesignal having a plurality of frequency components. The composite drivesignal is transmitted to the MEMS device via a single pair of driveleads. The MEMS device is designed such that each dimension of movementresponds to one or more intended frequency components according to itsresonant frequency and amplification factor, while minimizing responseto other frequency components.

According to another embodiment, two or more sinusoidal signals may becombined in a drive circuit and transmitted to a MEMS device as a singledrive signal.

According to another embodiment, one or more resonant signals may becombined with a non-resonant signal such as an approximately sawtoothwaveform, for example. For such an embodiment, a non-resonant member maybe directly driven while one or more resonant drive signals arepropagated through the structure. To prevent the non-resonant signalfrom exciting the resonant body, frequency components near the resonantfrequency of the resonant body are eliminated from the non-resonantsignal. This may be conveniently accomplished, for example, by includingonly lower order harmonics in the non-resonant signal.

According to another embodiment, a MEMS drive signal generator includesprovision for generating and combining a plurality of frequencycomponents.

According to another embodiment, a moving magnet MEMS actuator includesa magnet mounted on suspension elements. The suspension elements spreadthe torque load across the active surface of the device and thus limitdistortion.

According to another embodiment, a moving magnet MEMS actuator mayinclude a moving system having antiparallel magnetic fields. A singleelectromagnet may induce rotation about one or more axes bysimultaneously attracting one field while repelling the other.

According to another embodiment, an improved MEMS scanner may be used ina scanned beam imager.

According to another embodiment, an improved MEMS scanner may be used ina scanned beam display.

According to another embodiment, an improved MEMS scanner may be used toproduce a corrected scan path. The scanner may include three or moredegrees of freedom, each of which responds to a drive signal accordingto its resonant frequency and amplification factor. Thus, it ispractical to drive three or more scan axes (some of which may besubstantially parallel) without the complication of providing three setsof drive leads and three actuators. The drive signals are propagatedthrough the scanner using the off-resonance response of intermediatestructures.

Other aspects of the invention will become apparent according to theappended drawings and description, to be limited only according to theclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of a magnetic drive MEMS scanner having twoscanning axes driven by moving coils wired in series.

FIG. 2A is a sectional view of the MEMS scanner of FIG. 1 showingmagnets for generating a magnetic field.

FIG. 2B is a sectional view of the MEMS scanner of FIG. 1 showinganother embodiment of magnets.

FIG. 2C is a sectional view of the MEMS scanner of FIG. 1 showinganother embodiment of magnets.

FIG. 2D is a sectional view of the MEMS scanner of FIG. 1 showinganother embodiment of magnets.

FIG. 2E is a sectional view of the MEMS scanner of FIG. 1 showinganother embodiment of magnets.

FIG. 3A is a view of a magnetic drive MEMS scanner having two scanningaxes driven by a single moving coil and having a single pair ofbiaxially compliant support arms.

FIG. 3B is a detailed view of the drive coil and sense coil pass overand passunder of FIG. 3A.

FIG. 3C is a detailed view of the outer drive coil and sense coil leadsof FIG. 3A.

FIG. 4A is a view of a magnetic drive MEMS scanner having two scanningaxes driven by a single moving coil on the gimbal ring.

FIG. 4B is a side view of a MEMS scanner illustrating dynamicdeformation of an unsuspended scan plate.

FIG. 4C is a side view of a MEMS scanner showing reduced dynamicdeformation in the scan plate achieved by using a suspension.

FIG. 4D illustrates an embodiment wherein a suspension forms acontinuous structure around an inner scan plate.

FIG. 5 is a view of a single axis MEMS scanner driven throughsympathetic resonance from a piezoelectric actuator.

FIG. 6 shows individual and multiplexed waveforms for driving a two-axisMEMS scanner.

FIG. 7A is a block diagram of a driving circuit for driving a single orseries actuator to induce movement in two axes.

FIG. 7B is a block diagram of a MEMS controller that includes provisionfor position feedback.

FIG. 8 is a view of a single axis moving magnet scanner.

FIG. 9 is a view of a two-axis moving magnet scanner having opposedfixed magnetic fields.

FIG. 10 is a block diagram of a scanned beam imager with a MEMS scanner.

FIG. 11 is a diagram of a scanned beam display.

FIG. 12A is a diagram of information presented to the user of thescanned beam display of FIG. 11 when used in a see-through mode.

FIG. 12B is a diagram of information presented to the user of thescanned beam display of FIG. 11 when used in an occluded mode.

FIG. 13 is a beam position diagram showing the path followed by thescanned beam in response to a ramped vertical scan exemplified byindividual waveforms 602 and 608 and combined waveform 610 of FIG. 6.

FIG. 14 is a Lissajous scan pattern that may be created by a correctionmirror resonating at twice the frequency of a fast scan mirror.

FIG. 15 is a beam position diagram showing a corrected scan path formedby superimposing the pattern of FIG. 14 over a linear vertical scan.

FIG. 16 is a response curve of a simple resonant body.

FIG. 17 shows response curves for two modes of a resonant body.

FIG. 18 shows response curves for coupled modes between two resonantbodies. The resonant frequencies are widely separated and there isminimal perturbation of the curve shapes.

FIG. 19 is a mechanical model for a MEMS device having two oscillatorymasses.

FIG. 20 shows response curves for coupled modes between two resonantbodies. The resonant frequencies are relatively similar and the curvesinduce perturbations in one another.

FIG. 21A shows differential equations for describing the dynamicmovements of the indicated system, a simplification of the systemrepresented by FIG. 19.

FIG. 21B is a plot of response curves for coupled modes between tworesonant bodies of a real MEMS device. The resonant bodies have resonantfrequencies that are relatively close together and the bodies induceperturbations in the response of one another.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates an embodiment according to the invention having aseries actuator that carries drive signals for a plurality of axes.Mechanical motion for the various axes is determined by the matching ofdrive signal frequency components to the mechanical resonance of eachaxis.

MEMS scanner 102, here embodied as a beam scanner or beam director,comprises various structures etched or formed in a silicon die. Outersupport structure 104 acts as a frame to anchor the scanner to othermounting features (not shown) and includes pads (not shown) forreceiving drive signals and traces for transmitting the drive signals tothe actuator(s). Support structure 104 may further include traces andpads for providing drive current to sensors and transmittingposition-sensing signals to a controller.

Outer support frame 104 supports gimbal 106 on torsion arms 108 a and108 b. As is conventional, the terms “gimbal” and “gimbal ring” are usedinterchangeably herein. It should be understood that a variety ofspecific structures may act as a gimbal including open and closed-endrings, and other non-ring type structures that allow controlled movementabout selected axes.

Torsion arms 108 a and 108 b allow gimbal ring 106 to rotate about axis110 as indicated by arrow 111. Suspended within gimbal 106 is oscillatoror scan plate 112, which may for example take the form of a plate thathas a mirror 113 formed thereon. In the description herein, the terms“oscillator” and “scan plate” may be used interchangeably for manypurposes. Torsion arms 114 a and 114 b couple scan plate 112 to gimbalring 106, and allow the scan plate to rotate about axis 116 as indicatedby arrow 117. As is apparent, axis 116 is fixed relative to the gimbalring 106 and rotates along with the gimbal ring relative to supportframe 104

As an alternative or in addition to mirror 113, scan plate 112 may haveone or more electromagnetic energy sources formed thereon, the movementproduced by scan plate 112 thus directly scanning one or more beams ofelectromagnetic energy. Such electromagnetic energy sources may emit anyor several of a broad range of wavelengths including gamma, x-ray,ultraviolet, visible, infrared, microwave, or radio. For ultraviolet,visible, and infrared emissions, the electromagnetic energy source (nowtermed a light source) may include one or more laser diode lightsources, such as conventional edge-emitting or vertical cavity emittinglasers for example, one or more LEDs, one or more fluorescent sources,or other types of emitters.

The mass and distribution of mass within scan plate 112 and thestiffness of torsion arms 114 a and 114 b determine a resonant frequencyand amplification factor for the rotation of scan plate 112 about axis116. Similarly, the combined mass of the assembly comprising gimbal ring106, torsion arms 114 a and 114 b, and scan plate 112 (and their massdistribution); and the stiffness of torsion arms 108 a and 108 bdetermine a resonant frequency and mechanical amplification factor (alsocalled simply “amplification factor”) for the rotation of the scan plateand gimbal assembly about axis 110. In general, the designer has widelatitude in choosing a resonant frequency and amplification factor foreach of the two axes. For a two-axis (and by analogy, multi-axis) MEMSscanner 102, the resonant frequency of scan plate 112 rotation aboutaxis 116 may be selected to be significantly higher than the resonantfrequency for the assembly's rotation about axis 110.

Actuator 118, embodied as a coil in the example of FIG. 1, may be drivento produce rotation of gimbal ring 106 and suspended scan plate 112about axis 110. Similarly, actuator 120, also embodied as a coil, may bedriven to produce rotation of scan plate 112 about axis 116. Coils 118and 120 will act as actuators when MEMS scanner 102 is held in amagnetic field, such as that indicated as 124, that is transverse toboth axes 110 and 116. When coil 120 receives a signal that isperiodically driven at a rate corresponding to the resonance frequency(or any frequency that produces a suitable response) of scan plate 112,the amplitude of the rotation of scan plate 112 will be increasedproportionally to its amplification factor. In a similar manner, whencoil 118 receives a signal that is periodically driven at a ratecorresponding to the resonance frequency of the assembly comprising scanplate 112, torsion arms 114 a and 114 b, and gimbal ring 106; theassembly will oscillate about axis 110 with enhanced amplitude owing tothe mechanical amplification factor. By analogy, each resonancefrequency acts as a receiver tuned to receive a respective signal.

In alternative embodiments it may be preferable to provide a drivesignal corresponding to one or more harmonics of a MEMS member.Additionally, more complex waveforms may be used to achieve a desiredvelocity profile as the MEMS member sweeps through its range.

In the MEMS scanner 102 of FIG. 1, coils 118 and 120 are wired inseries. Alternatively, coils 118 and 120 could be wired in parallel. Ineither event, according to one embodiment, each coil responds to driveits respective element according to the resonance characteristics of itsassociated member. Thus a single signal to drive both axes is fed to thecoils via leads 122 a and 122 b. When the single signal containsfrequency components equal to each of the resonant frequencies of thesystem, each of the gimbal 106 and scan plate 112 will respondpreferentially to their individual characteristic resonant frequencies.In some systems, the actuators may respond with a characteristic 6 dBper octave roll-off or higher. Thus, with sufficient resonant frequencyseparation between the axes, each axis of rotation will substantially bedriven only at its resonant frequency.

In still other embodiments according to the invention, a scan plate,gimbal ring, etc. may be driven off-resonance. As will be explained inmore detail with respect to FIGS. 16-20, a suitable amount of movementin a member may be induced over a broad range of frequencies. Thus, theterm resonance, as used herein, is a shorthand way of referring to aresonant response that occurs over a range of frequencies, typicallypeaking at a single resonance frequency.

The actuators of FIG. 1 operate to generate a variable magnetic field.They are suspended in a magnetic field that is transverse to each of therotation axes 110 and 116. The example of FIG. 1 shows the transverse Bfield substantially in the nominal plane of the device. A magnetic Bfield, whose axis is indicated by arrows 124, may be generated usingvarious arrangements of electromagnets or permanent magnets. FIGS. 2Athrough 2E illustrate some of the possible arrangements of magnets, eachillustrated as a sectional view taken along section A-A′ of FIG. 1. Theorientation of the B field, as indicated by the direction of arrows 124,may be varied to achieve desirable operating characteristics, such assetting the desired response to various drive signals, or to suppressundesirable characteristics such as minimizing response in anundesirable axis or mode.

In FIG. 2A, magnets 202 a and 202 b are oriented with opposing magneticpoles facing one another across MEMS die 102. In FIG. 2B, the far polesof magnets 202 a and 202 b are joined by a keeper 204. The keeper 204 isoptimally constructed of a high magnetic permeability, high saturationmaterial such as steel, for example. A high permeability, highsaturation keeper can help to concentrate the magnetic field between thefacing poles of magnets 202 a and 202 b by reducing the fringing fieldaround each magnet to its opposite face. In FIG. 2C, the magnetic fieldis generated by a single magnet 202. The magnetic field is concentratedacross MEMS die 102 by opposing pole pieces 206 a and 206 b. Pole pieces206 a and 206 b are again optimally formed of a high magneticpermeability, high saturation material such as steel. FIG. 2Dillustrates use of a single magnet 202 that directs a fringing fieldacross MEMS die 102. FIG. 2E illustrates a single magnet formed on theback of a MEMS assembly. MEMS die 102 is joined to a spacer 208, forminga cavity 210 that allows for rotation of rotating parts out of plane.Magnet 202 is formed on the back of spacer 208. Spacer 208 may be formedof several materials including ferromagnetic materials such as steel andnon-ferromagnetic materials such as silicon or glass.

FIG. 3A illustrates an alternative embodiment of a MEMS scanner 102having two rotation axes 110 and 116. In the MEMS scanner of FIG. 3, asingle pair of biaxially compliant support arms 302 a and 302 b supportscan plate 112 and replace the separate pairs of torsion arms 108 a,band 114 a,b. The need for a separate gimbal ring 106 is thus eliminated.

The resonant frequency and amplification factor of scan plate 112 may beselected independently in each of the axes 110 and 116 by distributingits mass differently about each of the axes and by designing the supportarms 302 a and 302 b to have different torsional stiffness in each axis.For the example of FIG. 3, scan plate 112 may have a relatively highresonant frequency for rotation about axis 116 and a somewhat lowerresonant frequency for rotation about axis 110.

Mirror 113 is shown as a dotted line because for the particularembodiment of FIG. 3A, bare silicon is used as the reflective surface.Thus there is no mirror edge per se, but rather a mirror region that isdefined by the extent of a beam impinging upon the silicon surface. Thisdefined edge may vary depending upon particular beam alignment, shape,and size and depending upon the instantaneous angle of mirror 112relative to the beam. The effective mirror surface becomes more circularfor those instances when the mirror rotates toward the beam forming amore normal angle, and becomes more elliptical when the mirror rotatesaway from the beam.

Scan plate 112 includes a single drive coil 202 positioned peripherallyaround a mirror 113. The drive coil 202 is energized by leads 122 a and122 b. Although leads 122 a and 122 b are shown carried on differentsupport arms, they may alternatively be carried on a single arm. Leads122 a and 122 b may be connected to a drive signal having a plurality offrequency components. Drive coil 202 then receives each of the frequencycomponents. When drive coil 202 receives a frequency component equal tothe resonant frequency of axis 110, it drives scan plate 112 to rotateabout axis 110 at its resonant frequency. Similarly, when drive coil 202receives a frequency component equal to the resonant frequency of axis116, it drives scan plate 112 to oscillate about axis 116 at itsresonant frequency. Thus scan plate 112 may be driven substantiallyindependently to rotate about two axes at different frequencies.

For the particular embodiment of FIG. 3 a, the resonant (horizontal)scan frequency around axis 116 is 2.6 KHz. The resonant (vertical) scanfrequency around axis 110 is 0.8 kHz. The respective horizontal andvertical scan angles are 9.4° and 0.85°. There may be a small amount ofcrosstalk between the vertical and horizontal scan. For example, forrespective amplification factors of 500 to 1500, the vertical drive maycouple into the horizontal drive, resulting in a horizontal pixel offsetof approximately 3 pixels top-to-bottom. Varying the pixel clock orremapping the image may accommodate this where desired. Similarly, thehorizontal drive may couple into the vertical drive resulting into avertical pixel offset of approximately 0.7 pixel. This may beaccommodated by maintaining flexure symmetry, producing an asymmetry tocounteract the offset, or by image remapping. As noted below,introducing a correction mirror may further compensate vertical motion.The correction mirror may be designed to accommodatehorizontal-to-vertical drive coupling as well as raster pinch.

The MEMS scanner of FIG. 3A further includes a sense coil 303 upon whichdrive coil 202 is partially superimposed. The sense coil is connected toleads 304 a and 304 b. The sense coil is formed over or beneath drivecoil 202, as shown in FIGS. 3B and 3C, from a first metal layerseparated from the second metal layer of the drive coil by a dielectriclayer. The first metal layer additionally forms a pass-under for thesecond metal layer and the second metal layer forms a pass-over for thefirst metal layer. The sense coil undergoes induced current flow causedby its movement through the magnetic field. The current or voltage maybe sensed and the velocity or position of the scan plate and mirrordetermined therefrom.

Referring to detail sections 306 and 308 for the particular embodimentshown in FIGS. 3B and 3C, respectively, metal layer 1, indicated by thedarker traces, is comprised of deposited metal consisting of 1000angstrom TiW, 2400 ang Gold, 200 Ang TiW on 300 micron thick silicon,shown as the light gray region. The scan plate and support arm siliconis selectively backside etched to 80 micron thickness by timed deepreactive ion etching to reduce weight while forming reinforcing ribs tomaintain stiffness. A dielectric layer (not shown) is formed over metallayer 1. Metal 1 to Metal 2 connections are formed by leaving holes inthe dielectric layer at appropriate locations. Metal layer 2, indicatedby the lighter traces, is comprised of 10 micron thick gold. Metal layer2 is plated over the dielectric layer.

The sense coil 303, which lies under drive coil 202 for much of itspath, is formed in metal 1 (gold) and comprises 21½ turns. The sensecoil trace is approximately 12.5 microns wide with 10 micron spacing,yielding a coil resistance of 1.5 kilo-ohms. Sense coil enters scanplate 112 through trace 304 b, which terminates in a passunder 310 asshown in FIG. 3B. Metal 2 jumper 312 connects passunder 310 to the innerend 314 of sense coil 303. Sense coil spirals out in a counter-clockwisedirection and exits scan plate 112 at trace 304 a as shown in FIG. 3C.The choice of a counterclockwise-out spiral is arbitrary and could besubstituted by a clockwise-out spiral, resulting in a 180° difference insensed phase.

The drive coil 202, which lies over sense coil 303 for much of its path,is formed in metal 2 and comprises 9½ turns. The drive coil trace isapproximately 28 microns wide with 10 micron spacing, yielding a coilresistance of 12 Ohms. The drive coil enters scan plate 112 throughtrace 122 b as shown in FIG. 3A. Trace 122 b connects to metal 1passunder 316, which connects to the inner end 318 of drive coil 202.The drive coil spirals out in a clockwise direction and exits scan plate112 at trace 122 a as shown in FIG. 3C. As with the sense coil, thechoice of a clockwise-out spiral is arbitrary.

In one particular embodiment, scan plate 112 is suspended in a magneticfield oriented 30° to the right of axis 116 with a field strength of0.21 Tesla. Under these conditions, the sense coil produces a horizontalsense electromotive force (EMF) of 80 mV peak and a vertical sense EMFof 2 mV peak when the scan plate is driven at its designed angles andfrequencies. Other magnetic field angles may be used in some cases,depending upon the desired vector components of the magnetic fieldaccording to the application.

While the sense coil of the MEMS scanner of FIGS. 3A, 3B, and 3C couldbe used to sense motion in both axes, it may be desirable for someapplications to add piezo-resistive, photodetector, or other sensors tosense motion.

While FIG. 1 illustrates the case of a pair of series-wired drive coilsformed on both an inner scan plate and a gimbal ring and FIG. 3Aillustrates a single drive coil on an inner scan plate, FIG. 4Aillustrates the case of a single drive coil 202 on a gimbal ring 106with an inner scan plate 112 being induced to “ring” through mechanicalcoupling across its torsion arms 114 a and 114 b. Drive coil 202 rotatesthe assembly comprising gimbal ring 106 and inner scan plate 112 aboutaxis 110 directly. In this form, the drive signal for the resultant slowscan may be either resonant or may have another arbitrary shape. In someembodiments, the slow scan may be of a modified sawtooth form withprogressive movement around the axis alternating with a rapid fly-backto the starting position. When the drive signal also includes acomponent modulated at the resonant frequency of the inner scan plate112, the very slight mechanical response of the gimbal 106 getstransmitted across torsion arms 114 a and 114 b, through suspensionelements 402 a and 402 b, to scan plate 112. Owing to the resonantresponse of the inner scan plate, the transmitted movement amplified bythe system and result in resonant rotation of the inner scan plate aboutfast scan axis 116. When a mirror 113 is formed on inner scan plate 112,the resultant rotational movements may be used to direct a beam of lightacross a two-dimensional field of view.

Axes 110 and 116 may be placed at arbitrary angles to one another. Whilethe example of FIG. 4A (and other examples below) are shown having“nested” scanning masses oriented at 90° to one another, other anglesbetween 0° and 90° may be used. The inventors have discovered that driveimpulses at the resonant frequency of inner scan plate 112 couple quiteefficiently at various angles.

While gimbal support arms 108 a and 108 b are indicated as having aserpentine shape, straight, split, multiple and many other shapes oftorsion arms may alternatively be used. The scanner of FIG. 4A mayinclude piezo-resistive sensors in some or all of its torsion arms tomeasure position.

The inner scan plate 112 of FIG. 4A is illustrated supported by asuspension. The suspension transmits rotational torque between torsionarms 114 a and 114 b and suspended structure 112 while imposing acontrolled dynamic deformation on the suspended structure. In someapplications, and particularly some applications where the inner scanplate forms a base for a mirror 113, it is useful to impose a minimalamount of dynamic deformation on inner scan plate 112, thus keeping themirror as flat as possible for minimum optical distortion.

In the particular embodiments represented by FIG. 4A, the suspension 402includes a pair of suspension elements, or torque distribution members,402 a and 402 b, each connected to inner scan plate 112 at threelocations. As indicated in the Figure, suspension element 402 a includesan axial connection 404 a and two lateral connections, 405 a and 405 a′,through which torque is communicated with the inner scan plate 112.Similarly, suspension element 402 b includes an axial connection 404 band two lateral connections, 405 b and 405 b′, through which torque iscommunicated with the inner scan plate 113. In the case of oneparticular embodiment of FIG. 4A, axial connections 404 a and 404 b arerespectively smaller in cross section than torsion arms 114 a and 114 b.This limits the amount of torque concentration at the point where axialconnections 404 a and 404 b join inner scan plate 112 while eliminatinglateral or pumping modes of motion.

While the particular arrangement illustrated by FIG. 4A includesseparate suspension elements with three discrete connections to innerscan plate 112, a range of embodiments may be useful according to theapplication. For example, axial connections 404 could be increased insize or eliminated entirely. The number of discrete connections may beincreased. Alternatively, the connections between the suspension couldbe made continuous with compliance determined by the amount of thinningbetween the outer extent of the suspension and the outer extent of theinner scan plate. In continuous suspension connections, variablecompliance may be created by forming grooves of variable width orvariable spacing between the outer extent of the suspension and outerextent of the inner scan plate. The number of discontinuous suspensionelements may be increased above the two shown. Alternatively, thesuspension may form a continuous structure around inner scan plate 112.

FIG. 4B is a side view of dynamic deformation of a conventional MEMSscan plate driven by torque applied to the center of the scan plate.Scan plate 112 is shown at maximum deformation, the amount ofdeformation being exaggerated for ease of understanding. Torque 408 isapplied in a counterclockwise direction as shown, primarily by thetorsional spring 114 (not shown). At maximum deformation, torque fromthe torsion arm at axis 116 causes the scan plate to rotatecounterclockwise, while distributed inertial loads cause the ends of thescan plate to lag the center of the scan plate. It may be noted that forapplications where the scan plate is being driven through the torsionarm by one or more actuators, such as the example of FIG. 4A, torque 408is increased slightly relative to applications where the scan plate orsuspension itself is being driven; but for resonant scanning, the vastmajority of driving force is generated by energy stored in the springs(torsion arms).

FIG. 4C is a side view of a MEMS scanner showing reduced dynamicdeformation in the scan plate achieved by using a suspension. Scan plate112 is shown at maximum deformation, being driven counterclockwise aboutaxis 116. Lateral connections 405 (not shown) drive the scan platecounterclockwise as illustrated by tangential forces 410 a and 410 b.Additionally, axial connection 404 (not shown) drives the scan platecounterclockwise at axis 116 as shown by torque 408. Because suspensionmembers 402 themselves (not shown) are dynamically deformed such thatboth left and right ends are rotated clockwise relative to the scanplate (in a manner akin to the deformation of the un-suspended scanplate 112 of FIG. 4B), torques 412 a and 412 b are additionally appliedto the ends of the scan plate through respective lateral connections 405a and 405 b (not shown). The combined effects of torques 408 and 412 atend to drive the left side of scan plate 112 downward while thecombined effects of torques 408 and 412 b tend to drive the right sideof scan plate 112 upward, the effect of which helps keep the respectiveintermediate portions of scan plate 112 flat. Thus the use of asuspension partly or substantially overcomes the deformation related toinertial lag exhibited by the significantly deformed scan plate of FIG.4B.

FIG. 4D illustrates an embodiment wherein the suspension 404 forms acontinuous structure around inner scan plate 112. As shown in FIG. 4D,the suspension 404 extends to substantially surround the oscillator body112.

As implied above, because a large majority of the driving force in aresonant system comes from the stored energy in the torsion arms, theuse of a suspension may be used to help maintain scan plate flatness forplates that are driven directly as well as for plates that are driventhrough torsion arms.

While the examples shown heretofore have used moving-coil magneticallydriven actuators, other types of actuation technologies; includingmoving-magnet, electrocapacitive, piezoelectric, impact motor, fluid,and others; may be similarly multiplexed to generate movement inmultiple axes. Additionally, the principles taught herein may be appliedto driving single axis scanners through mechanical coupling acrosstorsion arms. FIG. 5 is an example of a multi-axis scanner mechanicallycoupled across a torsion arm to stacked piezoelectric actuators. Gimbal106 is suspended by torsion arms 108 a and 108 b. Torsion arm 108 aterminates at an anchor pad 502 a that is, in turn, attached to a fixedsubstrate 504. Torsion arm 108 b terminates at a drive pad 502 b that iscoupled to piezoelectric stacks 506 and 506′. Piezoelectric stacks 506and 506′ are mounted on fixed substrate 508 and are coupled to a drivesignal respectively by electrical traces 510 and 510′ at their lowerends and are coupled in series by an electrical trace on their upperends (trace not shown).

As an alternative to the example of FIG. 5, anchor pad 502 a could bemade into a drive pad by coupling it to a second pair of piezoelectricdrive stacks, thus driving the assembly through both torsion arms 108 aand 108 b.

Piezoelectric stacks 506 and 506′ may be such that when trace 510 is setto a higher voltage than trace 510′, the potential causes stack 506 toextend and 506′ to compress. When trace 510′ is set to a higher voltagethan trace 510, the opposite potential causes stack 506′ to extend andstack 506 to compress. By energizing traces 510 and 510′ with analternating periodic signal, piezoelectric stacks 506 and 506′alternately extend and compress in opposition to one another, causing aslight twisting motion of drive pad 502 b. In an alternativearrangement, piezoelectric stacks 506 and 506′ may be drivenindependently, each through a pair of leads.

The slight twisting motion of drive pad 502 b is transmitted astorsional stress through torsion arm 114 b to gimbal 106. For a givendrive frequency, the amplitude of movement of gimbal ring 106 (and otherstructures suspended therefrom) will be proportional to the voltage ofthe drive signal and to the mechanical amplification factor of therotating mass at the drive frequency (although not necessarily linearlyproportional). For drive frequency components at or near the resonancefrequency of the gimbal ring (and suspended structures), the rotation ofdrive pad 502 b will be amplified, a small amount of drive pad rotationcorresponding to a relatively larger rotation of gimbal ring 106. Foroff resonance drive frequency components, the amplitude of rotation ofthe gimbal ring is reduced and, at certain frequency ranges, inverted.

Gimbal ring 112 may be caused to oscillate periodically by introducingan asymmetry to the system. Such an asymmetry may include a massasymmetry about one or more axes of rotation (thus introducing a slightbending mode in the respective plate or gimbal), a rotation axisasymmetry (e.g. axis 116 not being at a perfectly right angle to axis110), or a drive asymmetry.

A drive asymmetry may be introduced by superimposing one or morein-phase frequency components to piezo stacks 506 and 506′. Such a driveasymmetry results in a slight upward-downward periodic motion of thedrive pad 506. This slight upward-downward periodic motion (which may beof the same or opposite sign compared to the upward-downward motion ofthe drive pad 506) is communicated through gimbal ring 106 as a slightrotation about axis 116. The rotation of gimbal ring 106 about axis 116is then amplified as a function of the mechanical amplification factorof gimbal ring 112 (with carried components including torsion arms 514a,b and inner scan plate 512), resulting in an intended rotation ofgimbal ring 112 about axis 116.

As may be seen, the mechanical coupling may be extended to additionalscan plates. Scan plate 112 acts as a gimbal ring for inner scan plate512, which is suspended from scan plate 112 by torsion arms 514 a and514 b. In the example of FIG. 5, inner scan plate 512 is formed torotate about axis 110. When the drive signal energizing traces 510 and510′ further comprises a frequency component equal to the resonantfrequency of scan plate 512, the slight twisting of drive pad 506arising therefrom is transmitted through torsion arm 108 b, gimbal ring106, torsion arms 114 a and 114 b, scan plate 112, and torsion arms 514a and 514 b to scan plate 512 so as to drive scan plate 512 to rotateabout axis 110 at a transmitted frequency where the mechanicalamplification factor of inner scan plate 512 results in rotation.

In some embodiments, scan plate 512 may include a mirror 113 formedthereon. One application for such a device is to create a raster pinchcorrection mirror in a 2D beam scanning system. The phase relationshipsbetween and amplitudes of the various frequency components of the drivesignal may be controlled. In a raster pinch correcting system, innerscan plate 512 may be designed to have a resonant frequency twice thatof scan plate 112. Its phase and amplitude may be selected to create avertical scan moving in opposition to and substantially equal to thevertical scan motion of gimbal 106 while scan plate 112 is traversingacross its scan range, and in the same direction as gimbal 106 whilescan plate 112 is at the end of its travel. Thus, the mirror 113 maydeflect a beam comprising substantially parallel paths in bothleft-to-right and right-to-left scanning directions, substantiallyeliminating raster pinch.

As may be seen, additional levels of scan plates may be nested anddriven without incurring the additional expense, yield loss, andelectrical loss associated with the formation of additional nestedactuators. One consideration is that successive scan plates are drivenvia at least minimal resonant response of intermediate plates, expressedin the primary axis of motion of the finally driven plate.

Alternatively, scan plates 112 and 512 could be eliminated and thesystem used to drive a single-axis scan plate 106. As may beappreciated, various combinations of the embodiments of FIGS. 1, 3A-3C,4A-4D, and 5 could be constructed within the scope of the invention.

As described above, the drive signals for actuating many of theembodiments according to the invention involve combinations ofwaveforms. By selecting mechanical amplification factors, resonantfrequencies, and drive signals acting on various portions of the MEMSapparatus, a broad range of design freedom may be enjoyed. FIG. 6 showsan example of waveforms for driving a plurality of oscillating elements.Waveform 602 is a high frequency signal for driving a first oscillatorcomponent at a corresponding high resonant frequency. Waveform 604 is alower frequency signal for driving a second oscillator component at acorresponding lower resonant frequency. Waveform 606 combines thesignals of waveforms 602 and 604. A signal corresponding to waveform 606may be transmitted to the actuator or actuators of MEMS scannersconstructed according to the invention. Each frequency component 602 and604 will thus actuate a particular oscillating element in accordancewith its resonant frequency and amplification factor.

Waveform 608 is a non-resonant signal for driving a scanner component ina non-resonant manner. Waveform 610 combines the signals of waveforms602 and 608. A signal corresponding to waveform 610 may be transmittedto MEMS scanners constructed according to the invention. When theamplification factor of a scanner component having a resonant frequencycorresponding to signal 602 is sufficiently high, the component willreject signals of different frequencies. Conversely, scanner componentsthat have low amplification factor will tend to receive a broad range ofsignals. Signal component 608 of waveform 610 may, for example, resultin a progressive scan and flyback of a low amplification factor gimbalring having a relatively large number of actuator coil windings whilesignal component 602 of waveform 610 drives its nested highamplification factor inner scan plate.

FIG. 7A is a block diagram of a signal generator that combinesindividual signal components into a drive signal for driving a MEMSscanner having components preferentially responsive to each of thesignal components. X-axis waveform generator 702 a and y-axis waveformgenerator 702 b each generate a respective signal for driving a MEMSscanner to move about the x and y-axes. Such movement may be rotational,translational, or other modes as appropriate for the application.Waveforms such as those shown in FIG. 6 may be used for example. Ifwaveform generator 702 a generates waveform 602 and waveform generator702 b generates waveform 604, they may be combined in multiplexer (MUX)706 to produce combined waveform 606. Alternatively waveform generator702 b may generate a non-sinusoidal signal such as waveform 608. In thatcase MUX 706 may combine the waveforms generated in waveform generator702 a and 702 b to produce a signal such as waveform 610. The combinedwaveform is transmitted to a MEMS actuator 708, which may be of manyforms including series coils 118 and 120 of FIG. 1, combined drive coil202 FIGS. 3A, 3B, 3C and 4, piezoelectric stacks 506 and 506′ of FIG. 5,or other types of actuators. As an alternative to discrete waveformgenerators 702 a and 702 b, an integrated device may produce drivewaveforms such that individual components (for example waveforms 602 and604) are not exposed or literally present.

FIG. 7B illustrates a MEMS drive block diagram having an integrated x-ywaveform generator 702 and a motion/position detector 710 connected to acontroller 712. Controller 712 issues waveform parameters to x-ywaveform generator 702. X-Y waveform generator 702 creates drivewaveforms and transmits them to a MEMS scanner 102 via drive traces 122.The physical position and/or motion is sensed and transmitted from theMEMS scanner 102 to a motion/position receiver 710 via sense traces 304.Motion position receiver 710 informs controller 712 of the motion and/orposition of the MEMS scanner. The controller may then maintain or modifythe waveform parameters sent to the x-y waveform generator dependingupon whether or not the MEMS scanner is performing the desired motion.Controller 712 may instruct the light source drive 714 to vary thesequential emission pattern of light source 716 to perform imageremapping to take into account the actual position of the mirror on MEMSscanner 102. Light source 716 emits a beam 718, which is deflected bythe mirror on MEMS scan plate 112 onto a field-of-view corresponding tothe sensed position of the scan plate.

While magnetic drive designs shown heretofore have been moving coiltypes, it is also possible to apply the principles described herein tomoving magnet MEMS designs. FIG. 8 shows a single axis moving magnetMEMS scanner having suspension elements for reducing mirror distortion.Scan plate 112 has mirror 113 on its surface. Scan plate 112 issuspended from torsion arms 114 a and 114 b, which, in turn, terminateat anchor pads 502 a and 502 b, respectively. Anchor pads 502 a and 502b are attached respectively to substrates 504 a (not shown) and 504 b.Drive magnet 802, which may be a permanent magnet or an electromagnet,is attached to the scanner assembly at attachment points 804 a and 804 bas indicated in the Figure. North and south poles of drive magnet 802are aligned respectively to the right and left sides of magnet asindicated in the Figure.

Actuator coil 806 is be placed below scanner 102 on its centerline asindicated. Alternatively, actuator coil 806 may be placed at a differentlocation such as in-plane or above scanner 102. Actuator coil 806 isenergized by leads 122 a and 122 b to create a variable magnetic Bfields 808. When electromagnet 806 is energized to produce a magnetic befield 808 oriented north up, the south pole of drive magnet 802 isattracted thereto and the north pole of drive magnet 802 repelledtherefrom, causing scanner 102 to rotate counterclockwise about axis116. Conversely, when electromagnet 806 drives magnetic field 808 southup, the south pole of drive magnet 802 is repelled and the north poleattracted, causing scanner 102 to rotate clockwise about axis 116.

Drive magnet 802 is affixed to the scanner assembly at attachment points804 a and 804 b as indicated. A moving magnet actuator and torsionspring energy storage can cooperate to generate a significant amount oftorque, which could distort mirror 113 if drive magnet 802 and torsionarms 114 a and 114 b were affixed directly thereto. Instead, attachmentof drive magnet 802 and torsion arms 114 a and 114 b to respectivesuspension elements 402 a and 402 b confines distortion to thesuspension elements, keeping mirror surface 113 flat as illustrated inFIGS. 4B and 4C. Suspension elements 402 a and 402 b may be attached tooscillating mass 112 in various arrangements. In some embodiments it maybe optimal to attach suspension elements 402 to oscillating mass 112 atthree points as indicated. Finite element analysis can aid the designerin selecting optimum attachment points.

As an alternative to suspending oscillating mass 112 from a pair oftorsion arms, various cantilevered or other designs may be substituted.

FIG. 9 shows a moving magnet embodiment of a two-axis MEMS scanner 102.As with the MEMS scanners of FIG. 8 and FIG. 5, anchor pads 502 a and502 b attach the assembly to mounting points. Torsion arms 108 a and 108b extending therefrom support gimbal ring 106. Gimbal ring 106, in turn,serves as an anchor for torsion arms 114 a and 114 b, which connect tosuspension elements 402 a and 402 b, respectively. Suspension elements402 a and 402 b connect to oscillating mass 112 which has a mirrorsurface 113 disposed thereon.

Two drive magnets 802 and 802′ may be affixed to gimbal ring 106 asshown to provide actuation force. Drive magnet 802 is attached to gimbalring 106 at attachment points 804 a and 804 b where the dotted linesrepresent locations on the bottom surface of gimbal ring 106. Similarly,drive magnet 802′ is attached to gimbal ring 106 at attachment points804 a′ and 804 b′. In some embodiments, it may be desirable to arrangethe north and south poles of drive magnets 802 and 802′ to beanti-parallel to one another as indicated. Such an arrangement allows asingle actuator to create opposing forces in the drive magnets forrotating the assembly around axis 110.

The moving magnet oscillating assembly of FIG. 9 is driven by anelectromagnetic actuator 806, which, for example, may be disposed belowthe plane of the MEMS scanner as indicated. As may be appreciated bythose having skill in the art, other positions for electromagnet 806 arealso possible. Drive magnet 806 is driven to produce a variable magneticB field 808 via leads 304 a and 304 b. When electromagnet 806 is drivento produce a variable magnetic field 808 with north up, drive magnet 802is attracted thereto while drive magnet 802′ is repulsed therefrom. Thisproduces torsional force in the counterclockwise direction about axis110 and drives the scan plate to rotate counterclockwise. Conversely,when variable magnetic field 808 is driven south up, Drive magnet 802 isrepulsed and drive magnet 802′ is attracted, producing rotation in theclockwise direction about axis 110.

Various waveforms may be used to drive rotation about axis 110. Forexample, a sinusoidal waveform such as waveform 604 of FIG. 6 may, withproper frequency selection, produce resonant rotation about axis 110. Inother embodiments, a ramped waveform approximating a sawtooth waveform,such as waveform 608 of FIG. 6 may be used to produce non-sinusoidal,non-resonant motion.

As indicated above, one scan plate 112 is suspended from the gimbal ring106 on torsional arms 114 a and 114 b. As with other examples, the massdistribution of scan plate 112 and the stiffness of torsion arms 114 aand 114 b determine a resonant frequency and mechanical amplificationfactor for scan plate 112. In a manner similar to other examples,electromagnet 806 may be driven with a composite waveform comprising aplurality of frequency components.

Of note in the example of FIG. 9, is the asymmetry of the placement ofthe drive magnets 802 and 802′. Drive magnet 802 is mounted at its farend at outer position 804 b and its near end (respectively, as pictured)at inner position 804 a. The asymmetry of drive magnet 802′ is reversed,with its near end being mounted in an outer position 804 a′ and its farend mounted at an inner position 804 b′. This drive asymmetry results ina slight rotation of gimbal ring 106 about axis 116.

When variable B field 808 is driven with a frequency component having afrequency equal or near to the resonant frequency of scan plate 112,scan plate 112 will be sympathetically driven to oscillate about axis116. In a manner similar to the MEMS devices of FIGS. 4B and 5, slighttwisting of gimbal ring 106 about axis 116 is amplified by the resonantsystem of scan plate 112, creating torsional force through torsion arms114 a and 114 b. Though the overall twisting of gimbal ring 106 maybeslight, the amount of torque transmitted to scan plate 112, arising bothfrom driving torque and energy stored in torsion arms 114 a and 114 b,may be sizable. To reduce the tendency of this torsional force todistort scan plate 112, and hence mirror surface 113, suspensionelements 402 a and 402 b are interposed between scan plate 112 andtorsion arms 114 a 114 b, respectively.

Thus a composite drive signal such as waveforms 606 or 610 may be fedthrough leads 304 a and 304 b to produce movement in two or more axesaccording to the resonant properties of the oscillating components.

As described above, one or more other asymmetries including rotationaxis asymmetry and/or mass distribution asymmetry, could alternativelyor additionally be used to drive rotation of scan plate 112.

As an alternative to the sympathetic drive system of FIG. 9, each of thevarious oscillating components could be driven directly by placement ofdrive magnets thereon.

As with other examples presented herein, a DC bias current in coil 806in either direction will tend to shift the amplitude of rotation of thedriven member (i.e. gimbal ring 106 in the example of FIG. 9) to oneside or the other depending upon the direction of the DC bias. Thiseffect is especially pronounced with magnetic drive, owing to therelatively high drive torque of such systems. Such a DC bias current maybe used to vary or adjust the nominal direction in which mirror 103 isaimed. This may be useful, for example, to change the exit pupilposition of a scanned beam display or to pan the field-of-view for ascanned beam image capture device.

While FIG. 9 shows a two axis, two body scanner (i.e. a single scanplate and a single gimbal ring), it may be appreciated that the movingmagnet design may be readily applied to single-axis, greater than twoaxes, single-body, or greater than two bodies applications as well.

As mentioned earlier, the principles described herein may be applied tothe various MEMS Drive systems, magnetic or non-magnetic. For example,electrocapacitive drive pads or electrocapacitive interdigitated armscould be substituted for the drive magnets and electromagnets used inthe previous examples. Alternatively, thermal, fluidic, or otheractuation mechanisms could be substituted and remain within the intendedscope.

Various embodiments of MEMS scanners described herein may be employed toscan beams of light in a scanned beam image capture apparatus, scannedbeam displays, laser printer imaging systems, or other applications. Asimplified block diagram of a scanned beam image capture apparatus 1002is shown in FIG. 10. An illuminator 716 creates a first beam of light718. A scanner 102, having a mirror formed thereon, deflects the firstbeam of light across a field-of-view (FOV) to produce a second scannedbeam of light 1010. Taken together, the illuminator 716 and scanner 102comprise a variable illuminator 1009. Instantaneous positions of scannedbeam of light 1010 may be designated as 1010 a, 1010 b, etc. The scannedbeam of light 1010 sequentially illuminates spots 1012 in the FOV. Thescanned beam 1010 at positions 1010 a and 1010 b illuminates spots 1012a and 1012 b in the FOV, respectively. While the beam 1010 illuminatesthe spots, a portion of the illuminating light beam 1014 is reflectedaccording to the properties of the object or material at the spots toproduce scattering or reflecting the light energy. A portion of thescattered light energy travels to one or more detectors 1016 thatreceive the light and produce electrical signals corresponding to theamount of light energy received. The electrical signals drive acontroller 1018 that builds up a digital representation and transmits itfor further processing, decoding, archiving, printing, display, or othertreatment or use via interface 1020.

The light source 716 may include multiple emitters such as, forinstance, light emitting diodes (LEDs), lasers, thermal sources, arcsources, fluorescent sources, gas discharge sources, or other types ofilluminators. In one embodiment, illuminator 716 comprises a red laserdiode having a wavelength of approximately 635 to 670 nanometers (nm).In another embodiment, illuminator 716 comprises three lasers; a reddiode laser, a green diode-pumped solid state (DPSS) laser, and a blueDPSS laser at approximately 635 nm, 532 nm, and 473 nm, respectively.While laser diodes may be directly modulated, DPSS lasers generallyrequire external modulation such as an acousto-optic modulator (AOM) forinstance. In the case where an external modulator is used, it istypically considered part of light source 716. Light source 716 mayinclude, in the case of multiple emitters, beam combining optics tocombine some or all of the emitters into a single beam. Light source 716may also include beam-shaping optics such as one or more collimatinglenses and/or apertures. Additionally, while the wavelengths describedin the previous embodiments have been in the optically visible range,other wavelengths are within the scope of the invention.

As mentioned earlier, embodiments according to the invention may beapplied not only to scanning mirrors, but to other types of MEMS devicesas well. For example, a scan plate may have light emitters or a fiberoptic termination thereon in place of a mirror. Such devices may be usedto directly move the light beam in one or more axes in place of orauxiliary to a scanning mirror 103.

Light beam 718, while illustrated as a single beam, may comprise aplurality of beams converging on a single scanner 102 or onto separatescanners 102.

A 2D MEMS scanner 102 scans one or more light beams at high speed in apattern that covers an entire 2D FOV or a selected region of a 2D FOVwithin a frame period. A typical frame rate may be 60 Hz, for example.Often, it is advantageous to run one or both scan axes resonantly. Inone embodiment, one axis is run resonantly at about 19 KHz while theother axis is run non-resonantly in a sawtooth pattern to create aprogressive scan pattern. A progressively scanned bi-directionalapproach with a single beam, scanning horizontally at scan frequency ofapproximately 19 KHz and scanning vertically in sawtooth pattern at 60Hz can approximate SVGA resolution. In one such system, the horizontalscan motion is driven electrocapacitiveally and the vertical scan motionis driven magnetically. Alternatively, both the horizontal and verticalscan may be driven magnetically or capacitively. Electrocapacitivedriving may include electrocapacitive plates, comb drives or similarapproaches. In various embodiments, both axes may be driven sinusoidallyor resonantly. Other driving methodologies as described above or as maybe clear to one having skill in the art may alternatively be used.

Several types of detectors may be appropriate, depending upon theapplication or configuration. For example, in one embodiment, thedetector may include a PIN photodiode connected to an amplifier anddigitizer. In this configuration, beam position information is retrievedfrom the scanner or, alternatively, from optical mechanisms, and imageresolution is determined by the size and shape of scanning spot 1012. Inthe case of multi-color imaging, the detector 1016 may comprise moresophisticated splitting and filtering to separate the scattered lightinto its component parts prior to detection. As alternatives to PINphotodiodes, avalanche photodiodes (APDs) or photomultiplier tubes(PMTs) may be preferred for certain applications, particularly low lightapplications.

In various approaches, photodetectors such as PIN photodiodes, APDs, andPMTs may be arranged to stare at the entire FOV, stare at a portion ofthe FOV, collect light retro-collectively, or collect light confocally,depending upon the application. In some embodiments, the photodetector1016 collects light through filters to eliminate much of the ambientlight.

The scanned beam image capture device may be embodied as monochrome, asfull-color, and even as a hyper-spectral. In some embodiments, it mayalso be desirable to add color channels between the conventional RGBchannels used for many color cameras. Herein, the term grayscale andrelated discussion shall be understood to refer to each of theseembodiments as well as other methods or applications within the scope ofthe invention. Pixel gray levels may comprise a single value in the caseof a monochrome system, or may comprise an RGB triad or greater in thecase of color or hyper-spectral systems. Control may be appliedindividually to the output power of particular channels (for instancered, green, and blue channels) or may be applied universally to allchannels, for instance as luminance modulation.

Other applications for the MEMS scanners and actuation mechanismsdescribed herein include scanned beam displays such as that described inU.S. Pat. No. 5,467,104 of Furness et al., entitled VIRTUAL RETINALDISPLAY, which is incorporated herein by reference. As showndiagrammatically in FIG. 11, in one embodiment of a scanned beam display1102, a scanning source 1009 outputs a scanned beam of light that iscoupled to a viewer's eye 1104 by a beam combiner 1106. In some scanneddisplays, the scanning source 1009 includes a MEMS scanner with amirror, as described elsewhere in this document, that scans a modulatedlight beam onto a viewer's retina. In other embodiments, the scanningsource may include one or more light emitters that are rotated throughan angular sweep.

The scanned light enters the eye 1104 through the viewer's pupil 1108and is imaged onto the retina 1109 by the cornea. In response to thescanned light the viewer perceives an image. In another embodiment, thescanned source 1009 scans the modulated light beam onto a screen thatthe viewer observes. One example of such a scanner suitable for eithertype of display is described in U.S. Pat. No. 5,557,444 to Melville etal., entitled MINIATURE OPTICAL SCANNER FOR A TWO-AXIS SCANNING SYSTEM,which is incorporated herein by reference.

Sometimes such displays are used for partial or augmented viewapplications. In such applications, a portion of the display ispositioned in the user's field of view and presents an image thatoccupies a region 43 of the user's field of view 1204, as shown in FIG.12A. The user can thus see both a displayed virtual image 1206 andbackground information 1208. If the background light is occluded, theviewer perceives only the virtual image 1206, as shown in FIG. 12B.Applications for see-through and occluded displays include head-mounteddisplays and camera electronic viewfinders, for example.

As mentioned above in conjunction with the description of FIG. 5, oneuse of various embodiments of the MEMS scanners described herein is asraster pinch correcting scanners. FIG. 13 illustrates a scan path 1302followed by a scanned beam emitted by various devices including scannedbeam image capture devices as exemplified in FIG. 10 and scanned beamdisplays as exemplified in FIG. 11. Though FIG. 13 shows only elevenlines of image, one skilled in the art will recognize that the number oflines in an actual display or imager will typically be much larger thaneleven. As can be seen by comparing the actual scan pattern 1302 to adesired raster scan pattern 1304, the actual scanned beam 1302 is“pinched” at the outer edges of the field of view. That is, insuccessive forward and reverse sweeps of the beam, the pixels near theedge of the scan pattern are unevenly spaced. This uneven spacing cancause the pixels to overlap or can leave a gap between adjacent rows ofpixels. Moreover, because the image information is typically provided asan array of data, where each location in the array corresponds to arespective position in the ideal raster pattern 1304, the displacedpixel locations can cause image distortion.

To improve the quality of the image displayed or captured, it isdesirable to correct the “pinched” scan path 1302 to more nearlyapproximate the ideal raster pattern 1304. One way to do this is toprovide a separate beam path correction mirror as described in some ofthe patents cited and incorporated by reference near the end of thisdetailed description section. However, a separate correction mirror canhave undesirable cost, size, and complexity impacts. For manyapplications, it may be desirable to instead use a scanner assembly 102that includes a correction feature.

Referring back to FIG. 5, one may note that inner scan plate 512 withmirrored surface 113 may be driven to scan around axis 110 in commonwith outer gimbal 106. If inner scan plate 512 is driven at a frequencytwice that of horizontal scan plate 112 at a proper phase relationship,it may be appreciated (absent any motion by gimbal 106) that a scannedbeam reflected from mirror 113 could trace a “bow tie” or Lissajouspattern as shown by FIG. 14. Combining the Lissajous pattern of FIG. 14with vertical, substantially constant rotational velocity scanning bygimbal 106 produces the corrected scan pattern indicated by FIG. 15.FIG. 15 shows correction of the “pinched” scan path with a sinusoidalmotion of the correction mirror where the horizontal field of viewencompasses 90 percent of the overall horizontal scan angle. One skilledin the art will recognize that the error in position of the beam can bereduced further if the field of view is a smaller percentage of theoverall horizontal scan angle.

Correction scanners may be sympathetically or directly driven. Ofcourse, it is not necessary to use the stacked piezoelectric drivemechanism of FIG. 5. Other drive mechanisms including moving coilmagnetic, moving magnet magnetic, electrocapacitive, differentialthermal expansion, etc. may be used.

Further reductions in the scan error can be realized by adding one ormore additional correction mirrors to scanner 102. Such scan plates maybe added in a nested fashion as indicated in FIG. 5 or, with the use ofa “double bounce” or other beam path that returns the beam to the planeof the substrate of scanner 102, may be positioned laterally in eitheraxis to first scan mirror 113. Another approach to reducing the error isto add one or more higher order harmonics to the scanner drive signal sothat the scanning pattern of the inner scan plate 512, here acting as aresonant correction scanner, shifts from a sinusoidal scan closer to asawtooth wave that approximates more precisely the movement of gimbal106.

Other uses for various embodiments of the MEMS scanner described hereinwill be apparent to one having skill in the art.

Various embodiments of the MEMS scanner described herein may beintegrated into systems and/or combined with embodiments described inU.S. Pat. Nos. 6,140,979, entitled SCANNED DISPLAY WITH PINCH, TIMING,AND DISTORTION CORRECTION; 6,245,590, entitled FREQUENCY TUNABLERESONANT SCANNER AND METHOD OF MAKING; 6,285,489, entitled FREQUENCYTUNABLE RESONANT SCANNER WITH AUXILIARY ARMS; 6,331,909, entitledFREQUENCY TUNABLE RESONANT SCANNER; 6,362,912, entitled SCANNED IMAGINGAPPARATUS WITH SWITCHED FEEDS; 6,384,406, entitled ACTIVE TUNING OF ATORSIONAL RESONANT STRUCTURE; 6,433,907, entitled SCANNED DISPLAY WITHPLURALITY OF SCANNING ASSEMBLIES; 6,512,622, entitled ACTIVE TUNING OF ATORSIONAL RESONANT STRUCTURE; 6,515,278, entitled FREQUENCY TUNABLERESONANT SCANNER AND METHOD OF MAKING; 6,515,781, entitled SCANNEDIMAGING APPARATUS WITH SWITCHED FEEDS; and/or 6,525,310, entitledFREQUENCY TUNABLE RESONANT SCANNER; for example; all commonly assignedherewith and all hereby incorporated by reference.

Alternatively, illuminator 104, scanner 102, and/or detector 116 maycomprise an integrated beam scanning assembly as is described in U.S.Pat. No. 5,714,750, BAR CODE SCANNING AND READING APPARATUS ANDDIFFRACTIVE LIGHT COLLECTION DEVICE SUITABLE FOR USE THEREIN which isincorporated herein by reference.

As indicated above in conjunction with the discussion of FIGS. 1, 3A,4A, 5, 6, 7A, 7B, and 9, rotation or other movement about various axesis determined according to the physical response of the moving body. Inthose discussions, there was assumed to be little interaction betweenthe various axes of rotation or other movement. In real-world scenarioshowever the interaction between modes and moving bodies may besignificant.

FIG. 16 illustrates a simplified response curve 1602 for rotation of ascan plate having a resonant frequency f_(R). In this figure thevertical axis is denoted displacement amplitude, and indicates aphysical response. While a rotational response is plotted by the curve1602 of FIG. 16, other response modes may be similarly represented. Forexample, a “pumping mode” would involve up-down translational movement.The coupling between portions of scanners may thus be used to drivemodes other than rotation.

As is characteristic of many response curves, the displacement amplitudeof the oscillating body increases monotonically with frequency until itnears its resonant frequency, at which point the response climbs rapidlyto a finite level corresponding to mechanical amplification factor ofthe body at its resonant frequency. As frequency is increased furtherthe curve drops, sometimes precipitously, as the body is no longer ableto respond at the rate of the drive signal. It is frequently convenientto design systems to drive the MEMS device at or near its resonantfrequency to conserve energy and reduce power consumption.

Where the response curve of FIG. 16 indicates response of a singleoscillating body around a single axis, the response curves of FIG. 17show the response for a body around multiple axes. Here again, frequencyis plotted along the horizontal axis increasing to the right and thedisplacement response amplitude is plotted on the vertical axis withlarger displacement higher on the axis. The primary oscillatory responsecurve 1602 has a resonant frequency at f_(R1) and is similar in shape tothe response curve 1602 shown in FIG. 16. Also shown in FIG. 17 is asecondary oscillatory response curve 1702. Response curve 1702 indicatesthe response of the body along some other movement axis and represents asecond excitation mode. For the present discussion it is assumed theprimary oscillatory response 1602 measures rotation around an axisdefined by a pair of torsion arms. The secondary oscillatory responsecurve 1702 represents a tilting response for rotation about an axis inplane and orthogonal to the primary axis of rotation. The primaryoscillatory response may be envisioned as rotation about a pair oftorsion arms. The secondary oscillatory response can be envisioned astilting with the pair of torsion arms alternately bending up and bendingdown out of the plane of the device.

It should be noted that the secondary response curve 1702 displays asecond resonant frequency f_(R2) that may be the same as or differentfrom the primary mode resonance frequency f_(R1). For the presentdiscussion it is assumed that f_(R2) is somewhat higher in frequencythat f_(R1) and that the maximum displacement response amplitude in thesecondary axis (the mechanical amplification factor) is lower than theamount of response of the primary axis.

Referring now to FIG. 18, there is a relationship between various modesof motion of the various bodies of a MEMS device. Curve 1702 representsthe secondary resonant response of a first moving body. In this case thefirst moving body is a gimbal ring. As indicated in the earlier figures,the secondary response (corresponding to tilting about an axis 116,orthogonal to the gimbal ring support arm axis 110) increasesmonotonically as one increases frequency to f_(1R2) (i.e. the resonancefrequency of the first body in mode 2) corresponding to a singleresonance frequency of the system in the second movement response, andthen decreases monotonically as the drive frequency is raised further.For one real system the resonance frequency of curve 1702 is equal toapproximately 1500 hertz.

Superimposed over curve 1702, which represents tilting of the outerplate, is response curve 1802, representing rotation of an inner plate.For examples of physical embodiments one may refer to inner plate 112and gimbal ring 106 of FIG. 1 or 4. Thus, curve 1702 represents tiltingof the gimbal ring 106 about axis 116, and response curve 1802represents rotation of inner plate 112 also about axis 116. In theexample of FIG. 18, response curve 1802 increases monotonically withfrequency until it reaches a resonance frequency f_(2R1) (i.e. theresonant frequency of the second plate in rotation about axis 116). Asfrequency is increased further the response of the inner plate 112decreases. For one real system the resonance frequency f_(2R1) of curve1802 is about 20 kHz.

It is notable that the resonant frequencies of the two response curvesshown in FIG. 18 are relatively widely separated, at 1500 hertz and 20kHz respectively for curves 1702 and 1802. This may be seen frominspection of point 1804 on curve 1802, corresponding to the resonancefrequency of curve 1702, and inspection of point 1806 on curve 1702,corresponding to the resonance frequency of curve 1802. In each case theshape of the curve is relatively unaffected by the resonance of theother plate, each curve instead resembling the “pure” responses of FIGS.16 and 17.

Thus, when the outer plate is driven at f_(2R1) of 20 KHz, it tilts veryslightly according to the displacement amplitude of curve 1702 at thatfrequency, but induces a sizable displacement in the inner plate, whichrotates significantly according to the displacement amplitude of curve1802 at that frequency. This energy transfer is indicated by arrow 1808.This situation corresponds to the cases described earlier, whichreferred to very slight displacement of one member inducing sizabledisplacement in another member.

When resonance frequencies of various components of the MEMS system arecloser together, other interactions may occur, with each resonance modeaffecting the response of the other modes. Before looking at the shapesof curves for such interactions, we refer to FIG. 19, which shows oneway to model the mechanical system.

In the model of FIG. 19, a base 504, corresponding to a mounting pointof the system, is elastically coupled to a first mass M1 106(corresponding for example to a gimbal ring) through a spring withstiffness k₁ and with energy dissipation (non-elastic response)represented by coefficient c₁. These are modeled respectively as aspring 108 and a dash pot 1902. A force F₁ (not to be confused withlowercase f, used to designate frequency), corresponding to an actuator,may act to displace mass M1 from its rest position. Spring 108 will actto restore mass M1 to its rest position, as modified by the dampingaction of dash pot 1902.

In this example, spring 108 is numbered to correspond to torsion arms108 a and 108 b of FIGS. 1 and 4. Correspondingly mass M1 106 isnumbered to correspond to gimbal ring 106 of the same figures. While theprimary displacement of mass M1 106 in response to force F₁ is, at manyfrequencies, rotation about axis 110, one may recognize that mass M1 106may also be displaced in an orthogonal axis of rotation, i.e. in atilting mode about axis 116. For the present analysis, the main mode ofinterest is the secondary mode of tilting about axis 116.

Connected to mass M1 106 is a second mass M2 112. Mass M2 may be modeledas being connected to mass M1 via a spring 114 having a spring constantk₁₂ and a dash pot 1904 having a damping coefficient C₃. Taken in thecontext of FIGS. 1 and 4, mass M2 112 may be seen to correspond to innerscan plate 112 and spring 114 may be seen to correspond to torsion arms114 a and 114 b. Mass M2 112 further interacts with base 504 throughdash pot 1906 having a damping coefficient C₂. Damping coefficients C₁,C₂ and C₃ correspond to energy dissipation mechanisms of the system. Inparticular, C₁ corresponds to two primary effects: energy dissipationthe mounting between the MEMS die 102 and base structure 504, and gasdamping acting on the gimbal ring. C₂ corresponds primarily to gasdamping acting on the inner scan plate 112. C₃, which correspondsprimarily to energy dissipation in the torsion arms due to the relativemotion of M1 and M2, is usually negligible and is therefore ignored whenmodeling the system.

As with displacement of mass M1 106, mass M2 112 may be displaced by aforce F2. Upon such displacement, spring 114 tends to restore mass M2 toits resting position with respect to mass M1 as a function of its springconstant k₁₂ as modified by the damping coefficient C₂ of dash pot 1906.It can be appreciated that a force F2 acting on mass M2 112 may distendnot only spring 114 but also spring 108, depending on the ratio of theirrespective spring constants k₁₂ and k₁. Under static conditions, forceF1 acts only on spring 108 but not on spring 114. Rather the combinedinertia of masses M1 106 and M2 112 tend to oppose force F1 underdynamic conditions. Also under dynamic conditions, it can be appreciatedthat interactions between the various components of the system mayproduce complex relationships between the movement of mass M1 and massM2.

Several simplifying assumptions may be made to ease modeling. Theseinclude linear behavior of springs and damping (including nohysteresis), massless springs, linear behavior of the drive forces, andconstants that remain constant with various environmental changesincluding temperature. For some systems, especially systems that undergolarge displacements, such simplifying assumptions may not beappropriate, as is known to those having skill in the art. Using thelisted simplifying assumptions, dynamic movements of the systemrepresented by FIG. 19 are governed by the differential equations 2102and 2104 given in FIG. 21A.

According to the differential equations shown above, when the systemcorresponding to FIG. 19 is driven periodically by force F1, motion ofboth masses M1 106 and M2 112 will result. For example when F2 is set tozero (i.e. F2=0) and F1 is driven in a sine wave (F2=F0*sin(2πf*t)),where F0 is the load amplitude, f is frequency, and t is time, themotion of the two masses may respond as shown by curves 1702 and 1802 ofFIG. 20.

As with FIG. 18, curve 1702 represents the tilting mode of the gimbalring while curve 1802 represents rotation of the inner scan plate. Withrespect to the model of FIG. 19, curve 1702 also corresponds todisplacement of mass M1 106 and curve 1802 corresponds to displacementof mass M2 112 on common displacement axes. In accordance with thestructures of FIGS. 1 and 4, the common displacement axis 116 isexhibited as tilting of the gimbal ring in the case of curve 1702 androtation of the inner scan plate in the case of curve 1802.

Curve 1702 rises monotonically until it reaches the resonant frequencyf_(1R2) of the tilting mode of the gimbal ring. It then decreases withfurther increases in frequency. It does not, however, decreasemonotonically as with the system of FIG. 18. Rather, its shape isaffected by the response of curve 1802. In other words, the dynamicresponse of mass M1 106 is affected by the dynamic response of mass M2112 as dictated by the spring constants, damping coefficients, andmasses of the model of FIG. 19. It should be emphasized that the valuesused in the model correspond to real characteristics of the MEMS device.

Curve 1802 exhibits corresponding interaction with curve 1702. Inparticular, rather than the curve monotonically increasing until mass M2reaches its resonant frequency f_(2R1), curve 1802 shows a peak inresponse 1804 corresponding to the resonant frequency f_(1R2) of thegimbal ring in tilting mode, as represented by curve 1702. In a physicalsystem, the corresponding peaks at f_(1R2) represent in-phase movementof the scan plate 112 and the gimbal ring 106 about axis 116.

As indicated by arrow 2002 the tilting of the gimbal ring transfersenergy to the inner scan plate in the form of rotation. Thus, atf_(1R2), an actuator physically coupled to the gimbal ring may be usedto drive rotation of the scan plate.

As can be seen from FIG. 20, in coupled systems having relativelysimilar resonant frequencies, the scan plate may be driven at a resonantfrequency of the gimbal ring. For this example, the resonant frequencyis that of tilting about axis 116. In principal, however, other modesand other resonant frequencies may be similarly used.

At a higher frequency f_(2R1) near the resonant frequency of inner scanplate 112 in rotation, a corresponding phenomenon may be observed as maybe seen from inspection of curve 1702 of FIG. 20. At a frequency belowbut approaching the resonance frequency of the inner scan plate 112 inrotation, a local minimum is observed in curve 1702. Continuing higherin frequency, the tilting response of the gimbal ring then increases toreach a local maximum near the resonant frequency of rotation of theinner scan plate 112, f_(2R1). At this point, as indicated by arrow1808, energy is transferred to the inner plate to create a maximum inits displacement amplitude. In the case of present example, thisdisplacement amplitude is exhibited as rotation about axis 116 of theinner scan plate 112 relative to the gimbal ring 106.

Whereas the coupling between curves 1702 and 1804 was in phase atresonance frequency f_(1R2), the coupling at f_(2R1) is out of phase.That is, when scan plate 112 is rotated clockwise by an amountcorresponding to the displacement amplitude of curve 1802, the gimbalring is tilted counterclockwise by an amount corresponding to thedisplacement amplitude of curve 1702. Thus, while the curves 1702 and1802 resulted in additive displacement of the mirror surface atfrequency f_(1R2), the direction of displacement of curve 1702 atfrequency f_(2R1) is in opposition to the direction of displacement ofcurve 1802.

FIG. 21A shows differential equations 2102 and 2104 for describing thedynamic movements of indicated system, a simplification of the systemrepresented by FIG. 19. FIG. 21B shows the theoretical frequencyresponse curves on a dB scale of a real system according to thedifferential equations describing the system of FIG. 19 shown above. Theamplitudes are absolute values calculated relative to an external fixedreference frame. At frequency f_(2R1), the scan plate scan amplitude is7, while the gimbal ring oscillation amplitude is 2. The angles of thetwo bodies have approximately 180 relative phase at f_(2R1).

While driving the system at a point corresponding to the local minimumof curve 1702 would result in a higher effective ratio of (mirroramplitude response to gimbal ring amplitude response) mechanicalamplification factors, he response of the inner scan plate was notsufficient to generate an acceptable scan angle.

Another candidate frequency for driving the system corresponds tof_(1R2), where the responses of the gimbal ring and the inner scan plateare approximately in-phase relative to one another. At this frequency(about 1700 hertz) the system exhibited its highest response of 25° and20° respectively for curves 1802 and 1702. However, the horizontal scanrate (i.e. about 1700 hertz) was not sufficient to meet other systemrequirements.

While the examples discussed herein have related to scanning phenomena,and particularly rotation of an inner scan plate suspended by an outergimbal ring exhibiting tilting, other types of motion may be similarlycoupled. Various modes of oscillation as are known to the art may beuseful in a variety of applications. For example vertical translationmay be used by a variety of systems, including optical focusingapplications, range finding applications, or other embodiments were suchmotion is desired. Similarly, in-plane rotation, plate (vibrational)modes, and in-plane translation may be mechanically coupled to drive ascan plate through resonance. Additionally, similar phenomena may benoted with respect to coupled actuators such as the example of FIG. 1,multiply coupled bodies such as the example of FIG. 5, and with respectto parallel primary oscillatory axes such as the example of FIG. 5(where induced bodies 106 and 512 both rotate about axis 110).

The preceding overview of the invention, brief description of thedrawings, and detailed description describe exemplary embodiments of thepresent invention in a manner intended to foster ease of understandingby the reader. Other structures, methods, and equivalents may be withinthe scope of the invention. As such, the scope of the inventiondescribed herein shall be limited only by the claims.

1-25. (canceled)
 26. A MEMS oscillator, comprising: a frame; a first setof support arms coupled to the frame; a gimbal coupled to the first setof support arms; an actuator positioned to drive the gimbal to rotatearound an axis defined by the first set of support arms; a second set ofsupport arms coupled to the gimbal; and an oscillating body coupled tothe second set of support arms to receive a drive impulse through thesecond set of support arms from the gimbal so as to be driven tooscillate around an axis defined by the second set of support arms. 27.The MEMS oscillator of claim 26, wherein; the oscillating body iscoupled to receive drive impulses at its resonance frequency through thesecond set of support arms; and the oscillating body is positioned tooscillate at its resonance frequency.
 28. The MEMS oscillator of claim26, wherein the actuator is positioned to directly drive the gimbal. 29.The MEMS oscillator of claim 26, wherein the actuator is a moving coilmagnetic actuator.
 30. The MEMS oscillator of claim 26, wherein theactuator is a moving magnet magnetic actuator.
 31. The MEMS oscillatorof claim 26, wherein the actuator is an electrocapacitive actuator. 32.The MEMS oscillator of claim 26, wherein the first set of support armscomprises two torsion arms.
 33. The MEMS oscillator of claim 26, whereinthe second set of support arms comprises two torsion arms.
 34. The MEMSoscillator of claim 33, wherein the second set of support arms arecoupled to the oscillator body through at least one suspension element.35. The MEMS oscillator of claim 26, wherein at least one of the firstset of support arms and the second set of support arms is a singlecantilevered arm.
 36. The MEMS oscillator of claim 26, wherein the axisof rotation defined by the second set of support arms is transverse tothe axis of rotation defined by the first set of support arms.
 37. TheMEMS oscillator of claim 36, wherein the axis of rotation defined by thesecond set of support arms is substantially at a right angle to the axisof rotation defined by the first set of support arms.
 38. The MEMSoscillator of claim 26, wherein the oscillating body further comprises:a second gimbal; a third set of support arms coupled to the secondgimbal; a second oscillating body coupled to the third set of supportarms to receive a drive impulse through the third set of support armsfrom the second gimbal so as to be driven to oscillate around an axisdefined by the third set of support arms.
 39. The MEMS oscillator ofclaim 26, wherein the oscillating body further includes a mirrorpositioned to receive a beam of light and deflect it across a field ofview. 40-46. (canceled)
 47. A MEMS device, comprising: an inner platehaving a principal oscillatory mode at a first frequency; an outer platehaving a secondary oscillatory mode at the first frequency; and acoupling between the inner plate and the outer plate selected to couplethe first frequency secondary oscillatory mode of the outer plate to thefirst frequency principal oscillatory mode of the inner plate.
 48. TheMEMS device of claim 47, wherein the principal oscillatory mode of theinner plate includes rotation about an axis defined by the coupling. 49.The MEMS device of claim 48, further including a mirror surface on theinner plate.
 50. The MEMS device of claim 48, wherein the outer plateincludes a gimbal structure.
 51. The MEMS device of claim 48, whereinthe outer plate includes an anchor structure.
 52. The MEMS device ofclaim 47, wherein the coupling includes a post.
 53. The MEMS device ofclaim 47, wherein the coupling includes a bending flexure.
 54. The MEMSdevice of claim 47, wherein the coupling includes at least one torsionarm.
 55. The MEMS device of claim 47, where the coupling includes asuspension to distribute the coupled first frequency oscillatory forceto a plurality of locations on the inner plate.
 56. The MEMS device ofclaim 47, further comprising an actuator operable to induce thesecondary oscillatory response in the outer plate at the firstfrequency.
 57. The MEMS device of claim 47, wherein the outer plate alsohas a primary oscillatory response at a second frequency.
 58. The MEMSdevice of claim 57, further comprising an actuator operable to induce inthe outer plate a secondary oscillatory response at the first frequencyand a primary oscillatory response at the second frequency.